1. Field of the Invention
The present invention relates to a seat belt device for use in restraining an occupant of a vehicle thus securing the safety against a traffic accident, and more particularly to an improvement of a tongue plate of a seat belt device.
2. Description of the Related Art
A tongue plate which allows the webbing to pass therethrough is engaged with a buckle, thereby fastening of the seat belt is effected. Examples of such a tongue plate are illustrated in Japanese Utility Model Laid-open Publications 151532/1977 and 42466/1994.
In an example illustrated in Japanese Utility Model Laid-open Publication 151532/1977, a webbing pass-through opening is constituted by an elongated hole which is formed linearly in the webbing width direction and both end portions of the elongated hole are formed of circular holes having a large curvature. Further, in an example illustrated in Japanese Utility Model Laid-open Publication 42466/1994, projecting portions are respectively formed on both end peripheries of a webbing and convex-shaped holes which correspond to the projecting portions are formed in both end portions of a webbing pass-through opening of a tongue plate. Due to such constitution, respective projecting portions formed on both end portions of the webbing are held in these two convex-shaped holes formed in the tongue plates thus preventing the twisting of the webbing.
However, when the circular holes having a large diameter are formed in both ends of the webbing pass-through opening as disclosed in Japanese Utility Model Laid-open Publication 151532/1977, there exists a possibility that the twisting of the webbing occurs. Further, when the convex-shaped holes formed in both ends of the webbing pass-through opening are directed toward the folding side of the webbing as disclosed in Japanese Utility Model Laid-open Publication 42466/1994, contact border lines with the tongue plate are defined slightly inside from both ends of the webbing in the width direction so that the peripheries of the webbing are worn. Particularly, when a fuse belt which can reduce a large load applied to an occupant at the time of collision is provided to a portion of the webbing in the vicinity of a webbing anchor plate, there arises a problem with respect to a manner to reduce the wear. To prevent the wear of both peripheral portions of the webbing, a method which increases the webbing pass-through opening in the webbing width direction may be considered. However, this method gives rise to the increase of the width of the overall tongue plate and the increase of the weight of the tongue plate and hence, the method is not preferable. Further, since the offset load is applied to the tongue plate, this method necessitates the reinforcement of the tongue plate to prevent the lowering of its strength. The reduction of the weight of the tongue plate, however small the reduction amount may be, is a matter to be taken into account for enhancing the winding characteristics of a retractor at the time of releasing the tongue plate.
Accordingly, it is an object of the present invention to provide a seat belt device which uses a tongue plate which can prevent its shape from becoming large-sized and can substantially prevent the occurrence of the twisting of a webbing and the wear of the peripheries of the webbing.
The above-mentioned object of the present invention can be achieved by a seat belt device which comprises a webbing which restrains an occupant to a seat, a tongue plate which allows the webbing to pass therethrough, a buckle which is positioned in the vicinity of a waist of the occupant and is engaged with the tongue plate, wherein the tongue plate includes a belt through portion in which a webbing pass-through opening which allows the webbing to pass therethrough is formed and an engaging portion which is engaged with the buckle, and the webbing pass-through opening includes a straight line portion which is linear in the webbing width direction and has an approximately constant width in the webbing thickness direction and first and second bent portions which have the approximately same width as that of the straight line portion and respectively extend in the oblique direction from both ends of the straight line portion toward a buckle engaging portion side.
Further, the above-mentioned object of the present invention can be also achieved by a seat belt device which is provided with a tongue plate to be engaged with a buckle, wherein the tongue plate comprises a first portion in which an opening to be engaged with the buckle is formed, a second portion which is offset by a given amount relative to the first portion in the thickness direction of the tongue plate and a connecting portion which connects the first portion and the second portion and in which a webbing pass-through opening is formed, and the webbing pass-through opening comprises a straight line portion which extends approximately linearly in the webbing width direction and a pair of bent portions which extend from both ends of the straight line portion toward the opening side to be engaged with the buckle.
Due to such constitution, when the webbing pass-through opening of the tongue plate which extends in the webbing width direction is comprised of the straight line portion and the bent portions which are raised toward the opening side from both ends of the straight line portion and the webbing is made to extend through the webbing pass-through opening in a slidable manner in the folded-back condition at a certain angle xcex1 (see FIG. 4), since the peripheral portions of the webbing are moved along the bent portions of the webbing pass-through opening which extended in the direction opposing the folding-back direction of the webbing, no strong force is applied to the peripheries of the webbing and hence, the generation of the wear to the peripheral portions of the webbing can be suppressed. Further, by making the width of the webbing pass-through opening in the webbing thickness direction approximately constant, the occurrence of the passing through of the webbing in a twisted form (and the turn-over of the tongue plate which may follow thereafter) can be prevented.
The length of the straight line portion of the webbing pass-through opening may preferably be approximately equal to or greater than the dimension of the webbing width.
Due to such constitution, when the webbing is not applied to the occupant, both ends of the webbing in the webbing width direction are not substantially brought into contact with the bent portions. Accordingly, the resistance which is generated when the webbing slides through the webbing pass-through opening of the tongue plate in the seat belt fastening step can be minimized and hence, the deterioration of the manipulating feeling in the belt fastening operation can be prevented.
Further, the overall dimension of the webbing pass-through opening in the webbing width direction is preferably set to a value which is greater than the width of the webbing and not more than the webbing width+6 mm.
Due to such a constitution, the deviation of the webbing can be prevented and an amount of offset load applied to the buckle in the webbing fastened condition can be reduced.